The ABO Blood Group System
- If you have A antigens covering your red cells then you have blood group A and you also have B-antibodies.
- If you have B antigens covering your red cells then you have blood group B and you also have A antibodies.
- If you have both A and B antigens covering your red cells then you have blood group AB and no A or B antibodies.
- If you have neither A or B antigens covering your red cells then you have blood group O and both A and B antibodies.
The Rhesus (Rh) system
Besides A and B there is another important antigen on red blood cells, the Rh antigen which is also known as the D-Antigen.
- If the Rh antigen is present, then the blood is RhD positive.
- If the Rh antigen is not present, then the blood is RhD negative.
The number of people who are Rh-positive varies by population:
In white Europeans about 16% of the population will have Rh negative blood types (and 8% will be Rh-positive). In the other populations of the world, the frequency of Rh negative types will be much lower; in Africans, only 9 people in 10,000 will be Rh negative, and in the non-African, non-European portion of the world, only 1 person in 10,000 will be Rh negative.
In the United States, about 15% of the general population is Rh negative; almost 20% of European Americans are Rh negative (because many Americans have western European ancestry), and approximately 5-10% of African Americans are Rh negative (because of the flow of European genes into the African American population). Fewer than 1% of Asian and Native Americans are Rh negative.